A standard bipin lamp, typically fluorescent, is fitted to a fixture having a pair of confronting, identical, and axially aligned sockets which each have a seat into which the two pins can be slid, and a pair of contacts that engage the respective pins when the lamp is properly seated. In order to hold the lamp in place, it is necessary to provide some structure that actually grips the contacts when the lamp is fitted properly in place or that captures the pins.
In a standard system, each socket is formed with a basically triangular and outwardly open slot. The two pins are aligned with a narrow mouth of the slot and pushed into it, then the lamp is rotated through about 90° so that the two pins move outward to press against the contacts that flank the slot and that are somewhat springy to press elastically against and hold the lamp. This is the simplest system and is only effective if the user can bet a good grip on the lamp so that it can be pivoted once it is fitted to the two sockets.
In many modern fixtures the lamp is, however, a very tight fit in the fixture so that there is really no room for the installer's fingers to engage around the lamp so as to be able to turn it. Thus as described in German utility model 94 09 147 published 10 Nov. 1994 it is known to provide a complex slide mechanism in each socket. The lamp is fitted to the slide mechanism and pressed inward, thereby actuating structure that engages and grips the lamp's pins. Such a system is fairly complex and adds considerably to the cost of the socket.
German patent 3,826,298 published 29 Jun. 1989 of Bushhoff describes another system where a sort of dielectric wrench is provided that is engaged with the lamp pins and that serves to pivot the lamp. Such an arrangement is inexpensive and highly effective, but requires that the user keep track of this wrench for installing and removing a lamp from the fixture. The wrench normally goes lost in the months or years between lamp changes, leaving the user with a nearly impossible job in getting out the old lamp and installing a new one.